The menisci are fibrocartilaginous structures in the knee that frequently tear with age. Meniscal tears occur in one third of individuals over 50 years old and in 80% of patients with knee osteoarthritis (OA). The vast majority of these tears are asymptomatic. The patient-reported outcomes of surgical and nonoperative therapy for meniscal tear are poorly studied. Surgery (arthroscopic partial meniscectomy; APM) appears to be associated with accelerated osteoarthritis, but it is unclear whether the true risk factor is surgey per se or the underlying meniscal lesion. In 2007, we received 5-year funding from NIAMS to conduct the MeTeOR Trial (Meniscal Tear in Osteoarthritis Research). The goal of MeTeOR was to establish whether APM leads to better functional status than nonoperative treatment of patients with meniscal tear and osteoarthritic changes 6 and 24 months following enrollment. The MeTeOR trial completed enrollment in August 2011 by randomizing 351 subjects in seven centers. Continued follow-up beyond 24 months is critical to determine whether surgery results in longer-term improvement in pain and function and whether surgery is independently associated with accelerated structural progression. More fundamentally, there have been no longitudinal, comprehensive studies of individuals with symptomatic meniscal tear and osteoarthritis changes. Continued follow-up of this cohort is needed to identify predictors of symptomatic, functional and structural progression in these patients. We propose the following specific aims: 1) Characterize changes in knee pain and functional status in operatively and nonoperatively treated MeTeOR patients over 5-year follow-up and identify factors associated with early response and with greatest loss of response to each treatment over time; 2) Characterize progression of cartilage damage over 5-year follow-up and identify factors associated with more rapid progression; 3) Conduct a cost-effectiveness analysis of APM compared with nonoperative therapy in patients with meniscal tear and concomitant OA over the 5-year time frame and over the remainder of patients' lives. We will achieve these aims by administering questionnaires to subjects every 6 months through 5 year follow- up. We will also obtain standardized magnetic resonance imaging studies and plain radiographs of the affected knee on all patients after 5 years of follow-up. The extended follow-up of the MeTeOR trial cohort provides an ideal opportunity to assess the success and cost effectiveness of APM and more generally to address key questions in the management of millions of people with symptomatic meniscal tear and osteoarthritis.